Encino, California – One hundred years ago this month, Woodrow Wilson ended America’s longstanding policy of isolation and led us into World War I on the Allied side. Over two and a half million Americans were shipped “over there” to Europe and served in the American Expeditionary Force (AEF). By war’s end, more than 100,000 Americans would join the ranks of what British Prime Minister Lloyd George termed, without a trace of irony, “the glorious dead.”

My own great-uncle John Wells (1895–1951) was a member of the AEF. Wells served as a 2nd Lieutenant in the 27th Infantry, or New York Division. He trained with the unit at Camp Wadsworth in South Carolina before deploying to Europe in May of 1918. In the fall of 1918, this unit saw fierce action in the Somme push and along the Meuse River. The New York Division helped to break the back of the German Army along the Hindenburg Line, leading to Germany’s surrender in November 1918.

Why did Wilson make his fateful decision to enter the “War to end all wars”?

Two of the principle reasons behind Wilson’s decision were the German policy of unrestricted submarine warfare and the Zimmerman Telegram.

Unrestricted submarine warfare has become a stilted phrase that smacks of dry textbooks and AP history examinations. It was not so then. The period prior to World War I was the golden age of ocean travel. Lindbergh did not fly across the Atlantic until 1927. The only practical way to travel between North America and Europe was via passenger ship. These passenger ships were the equivalent of commercial aircraft today.

Thomas Tileston Wells (John Wells’s father), for example, booked passage in 1909 on board the RMS Lusitania, which was destined to be sunk by a German U-boat off the coast of Ireland in 1915, killing around 1,200 passengers, including at least 125 Americans. In 1916, Germany moderated its submarine policy by pledging not to attack passenger ships without providing for the safety of their passengers and crew. But on January 31, 1917, Kaiser William II reversed course, ordering the resumption of unrestricted submarine warfare against Allied shipping. This desperate move helped tip the United States Congress, led by President Wilson, into declaring war on Germany on April 6, 1917.

In order to appreciate the full horror of unrestricted submarine warfare, imagine how we might react today if a warring nation state used its jet fighters to shoot down commercial airliners flying toward the cities of its enemy.

The Zimmerman Telegram is a reminder that much of the “surveillance society” in which we live today had its origins in World War I espionage. The British built a sophisticated signals intelligence network designed to monitor German radio traffic during the war. Room 40 was a decryption service of the British Admiralty that would later inspire the code breakers of Bletchley Park in World War II.

Their greatest coup of the war was the interception and decryption of the famous Zimmermann Telegram in 1917. This message, sent by the German minister of foreign affairs to the Mexican government, proposed an alliance with Mexico in the event of America’s entry into the war. Room 40 was also responsible for the capture of World War I’s most famous spy—the tragic case of Mata Hari.

World War I was enormously consequential for America and the world. The conflict cost over 17 million lives and was dubbed the “suicide of civilization” by Pope Benedict XV. This war toppled four empires and led directly to the creation of Syria and Iraq. The assassination of Archduke Ferdinand and his wife in Sarajevo had been the catalyst that first ignited the conflagration in 1914. But America entered the war in 1917 in response to issues that still resonate and have been further amplified in our own day—terror attacks on passenger travel and clandestine surveillance of and by foreign governments.